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I am running a graphics toolbox using Matlab called Psychophysics. I am this close to getting everything working, but I'm having drama with synchronization errors which has to do with my driver settings. Check this post out:

He says the error below is most likely due to a few options needed to be reset, most notably

Option "TripleBuffer"    "off"
Option "SwapbuffersWait"  "on"

My question is how do I even reset these values? He mentioned the xorg.conf file, but I've read in many different places that this file isn't used anymore. I can't find it using the 'find /usr -name xorg.conf' unix command on my system either (and that would take forever). I'm also afraid I will ruin my graphics card if I don't talk to someone who knows their stuff.

Here is my error message:

 PTB-INFO: No low-level controllable GPU on screenId 0. Beamposition
 timestamping and other special functions disabled.

 PTB-DEBUG:PsychOSGetSwapCompletionTimestamp: This likely means a
 driver bug or malfunction, or that timestamping support has been
 disabled by the user in the driver!

 PTB-INFO: OpenGL-Renderer is Intel Open Source Technology Center ::
 Mesa DRI Intel(R) Sandybridge Mobile  :: 3.0 Mesa 10.1.3 PTB-INFO: VBL
 startline = 768 , VBL Endline = -1 PTB-INFO: Will try to use
 OS-Builtin OpenML sync control support for accurate Flip timestamping.
 PTB-INFO: Measured monitor refresh interval from VBLsync = 16.682734
 ms [59.942213 Hz]. (297 valid samples taken, stddev=0.322476 ms.)
 PTB-INFO: Reported monitor refresh interval from operating system =
 16.646968 ms [60.070999 Hz]. PTB-INFO: Small deviations between reported values are normal and no reason to worry.

 WARNING: Couldn't compute a reliable estimate of monitor refresh
 interval! Trouble with VBL syncing?!?

 ----- ! PTB - ERROR: SYNCHRONIZATION FAILURE ! ----

 One or more internal checks (see Warnings above) indicate that
 synchronization of Psychtoolbox to the vertical retrace (VBL) is not
 working on your setup.
snoop
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lrthistlethwaite
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  • This X Wiki may help. If the conf file isn't present, the system is auto configured. If the file is present the settings in it are honored. – eyoung100 Jul 29 '14 at 20:41

2 Answers2

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Create a new file in /usr/share/X11/xorg.conf.d called any-name.conf. Put options in there. They get merged into the auto-generated xorg.conf when X starts.

Here's something from my machine:

% cat /usr/share/X11/xorg.conf.d/20-intel.conf
Section "Device"
  Identifier  "Intel Graphics"
  Driver      "intel"
  Option      "AccelMethod"  "sna"
  Option      "TearFree"    "true"
EndSection

Make sense?

user3113723
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I think I solved the issue relating to this.

I'll just walk through the steps here in this answer (I don't know if there's a better way though)

  • Get the latest intel drivers here and just click on the deb that opens the package manager and click install there. (This could take a lil while)

  • Go to the terminal and execute

    intel-linux-graphics-installer

  • Once done, reboot

Now we have to make the xorg.conf file. For this:

  • Create a file called xorg.conf in /etc/X11/. If xorg.conf already exists, back the old one up and create a new one. You will need superuser (sudo) access to edit this file

  • The contents of the xorg.conf follow

    Section "Device"
    Driver      "intel"
    Identifier  "PTB: generic TripleBuffer off"
    Option      "AccelMethod" "uxa"
    Option      "TripleBuffer" "off"
    Option      "SwapbufferWait" "on"
EndSection

  • Now log out and log in again.

Follow these steps and you must be good to go :) Let me know if you face any issues

SC

Sricharan Sunder
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    I'm excited you found it! I followed your instructions, but I found that my X11 folder was not in the /etc directory. It was in the same directory as /etc. I have the R2013b installation of MATLAB. I wonder if this is a mistake? This is how it was downloaded - I did not change the folder hierarchy here. I tried putting X11 in /etc and I tried a few other things. All still have VBL failures. Hmm. – lrthistlethwaite Aug 03 '14 at 04:02
  • Guy asked how to set xorg.conf values, not how to install drivers from intel, which may cause more problems. – user3113723 Dec 30 '15 at 04:28